Superinfection of latently Epstein-Barr virus (EBV)-carrying Raji cells with the P3HR-1 substrain EBV, known to induce the entry of a substantial fraction of cells into an abortively lytic cycle, increased the susceptibility of the cells to natural killer (NK) effect of human blood lymphocytes. Reciprocal cold-target competition tests with known NK-cell sensitive and -resistant lymphoid cell ines showed that the increased susceptibility is a result of the appearance of an NK-sensitive target, rather than to a general increase in membrane fragility. Lymphocytes of EBV-seropositive and -negative donors were equally effective killers against P3HR-1 virus-superinfected targets. EBV-induced NK sensitivity increased with time. It was a result of some event associated with the intracellular viral cycle, and not to the adherence of viral particles to the cell surface. Induction of EBV-carrying P3HR-1 cells to entry into the viral cycle with n-butyrate also increased their NK sensitivity. A transforming, noncytopathic prototype strain of EBV, B95-8, failed to increase the susceptibility of theRaji cells to NK-lysis, although it had some effect on the Daudi line. Because NK cells can kill virus-producing cells at an early stage of the cycle, before the virus particles are assembled, they may restrict, in vivo, the spread of the virus from latently infected cells.

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